The invention relates to a local area network operating in the asynchronous transfer mode (ATM) for transmitting cells, comprising a plurality of network nodes which are provided for forming a loop in the event of a defect of an assigned transmitting line or an adjacent network node.
Such a local area network (LAN) which operates in the asynchronous transfer mode is known from DE 195 32 442 C1. This network contains a plurality of ring systems with various network nodes which are mutually coupled in a ring system via a single or a double ring. The network nodes have station connections via which they are coupled either to a station or to another network. A network node detects a node failure or a line rupture when it no longer receives cells from a neighboring node via a line of a ring. In the event of a node failure or line rupture, the network node detecting this defect informs a network management system of the location of the line rupture. The network management system controls the reconfiguration of the network in that the system informs the network node whose transmitting line has a defect. This network node then forms a loop so that cells are no longer routed to the defective line, but to the other ring.
When an asynchronous transfer mode is used in a system, payload, for example, television, picture or sound signals, is transmitted in blocks of fixed length through arrangements for digital signal processing. A cell having a predetermined number of bytes (for example 53 bytes) is denoted a fixed-length block. Each cell comprises a header field having a length of 5 bytes and an information field in which the payload is accommodated having a length of 48 bytes. Such a header field are contains address information, data for fault detection and data for control indication bytes. Address information comprises trunk identifiers and link identifiers. For transmitting a cell, a virtual channel is rendered available based on the link identifier which is also referred to as a VCI (Virtual Channel Identifier). As a rule, a VCI is changed once it has reached a switching center. A group of virtual channels is denoted a virtual path (VPI=Virtual Path Identifier) featured by the trunk identifier.